- Email: [email protected]
Effects of twin-screw extrusion on soluble dietary fibre and physicochemical properties of soybean residue
Food Chemistry 138 (2013) 884–889
Contents lists available at SciVerse ScienceDirect
Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Effects of twin-screw extrusion on soluble dietary fibre and physicochemical properties of soybean residue Yan Jing, Yu-Jie Chi ⇑ Department of Food Science, Northeast Agricultural University, Harbin 150030, China Education Ministry’s and Provincial Key Laboratory of Soybean Biology, Harbin 150030, China
a r t i c l e
i n f o
Article history: Received 4 August 2012 Received in revised form 29 November 2012 Accepted 2 December 2012 Available online 8 December 2012 Keywords: Soybean residue Twin-screw extrusion Soluble dietary fibre Physicochemical properties
a b s t r a c t Extrusion cooking technology was applied for soluble dietary fibre extraction from soybean residue. Response surface methodology (RSM) was used to optimise the effects of extrusion parameters, namely extrusion temperature (90–130 °C), feed moisture (25–35%) and screw speed (160–200 rpm) on the content of soluble dietary fibre. According to the regression coefficients significance of the quadratic polynomial model, the optimum extrusion parameters were as follows: extrusion temperature, 115 °C; feed moisture, 31%; and screw speed, 180 rpm. Under these conditions, the soluble dietary fibre content of soybean residue could reach to 12.65% which increased 10.60% compared with the unextruded soybean residue. In addition, the dietary fibre in extrude soybean residue had higher water retention capacity, oil retention capacity and swelling capacity than those of dietary fibre in unextruded soybean residue. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The definition of dietary fibre (DF) proposed by the American Association of Cereal Chemists (AACC) defines DF as being made up of edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine (AACC Report, 2000). According to the solubility in water, total dietary fibre (TDF) can be categorised into two groups, namely soluble dietary fibre (SDF) and insoluble dietary fibre (IDF) (Vasanthan, Gaosong, Yeung, & Li, 2002). Many studies have shown that DF plays different physiological roles in human health and the SDF appears to be more effective than IDF in many healthy aspects (Esposito et al., 2005; Lou & Chi, 2009). But the most of crude dietary fibre are IDF, while the content of SDF are very low. Therefore, it has special significance to improve the SDF content of crude dietary fibre. Soybean residue is the main by-product from soymilk and tofu preparation, which is a good dietary fibre resource (Mateos-Aparicio, Mateos-Peinado, & Ruperez, 2010). The content of TDF in soybean residue is about 60%, while the SDF content is only approximate 2–3%. Extrusion cooking is a thermal processing that involves the application of high heat, high pressure, and shear forces to an uncooked mass, such as cereal foods (Kim, Tanhehco, & Ng, 2006). Extrusion technology is a new economical processing ⇑ Corresponding author at: Department of Food Science, Northeast Agricultural University, Harbin 150030, China. Tel./fax: +86 451 55191793. E-mail address: [email protected] (Y.-J. Chi). 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.12.003
methods, it can achieve protein, starch and cellulose polymer transformation directly or indirectly in a short time (Valentina, Paul, Andrew, & Senol, 2010). Extrusion of cereal-based products has advantages over other usual processing methods because of low cost, short time, high productivity, versatility, unique product shapes, and energy savings (Faraj, Vasanthan, & Hoover, 2004; Farouk, Pudil, Janda, & Pokoeny, 2000). In recent years, a number of researchers use barley flour and oat bran to prepare SDF (Vasanthan et al., 2002; Zhang, Bai, & Zhang, 2011). But there has no been relative reports about that using twin-screw extruder to prepare SDF from soybean residue. The results of our previous study (extrusion parameter: extrusion temperature, 160 °C; feed moisture, 20%; and screw speed, 175 rpm) also showed that the extrusion temperature of single screw extruder was too high, which consumed more energy and it is not benefit for industrial production. Therefore, the purpose of the present study was to employ response surface methodology to optimise the effect of different extrusion conditions on the content of SDF in soybean residue, thereby providing a reference for the preparation of high yield of soluble dietary fibre and its industrial production. 2. Materials and methods 2.1. Materials Soybean residue was supplied by bean products factory of Northeast Agricultural University (Harbin, China). Heat stable a-amylase, Protease and Amyloglucosidase were obtained from Sigma Chemical Company. All the other reagents were of analytical grade.
885
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889
2.2. Extrusion experiments
2.4. Experimental design
Soybean residue sample (1.5 kg) was extruded with a DS56-III twin-screw co-rotating, self-wiping extruder (Jinan Saixin Machinery Co., Jinan, China). The barrel diameter and length were 65 and 1008 mm, respectively, the screw speed up to 250 rpm. A screw configuration that was a standard design for processing cereals and flour-based products was used. This screw profile was made up of conveying self- wiping elements and the center distance of two screw was 56 mm. The feed moisture of 20%, 25%, 30%, 35% and 40% were selected according to the results of pre-experiments and references. The extrusion temperature was adjusted to 70, 90, 110, 130 and 150 °C, while screw speed of 140, 160, 180, 200 and 220 rpm were employed. The extruded soybean residue was dried in an oven at temperature of 60 °C, ground in a high speed disintegrator (Dade pharmaceuticals company, Wenzhou, China) to obtain a fine power (Particle size: 0.425 mm), then stored at room temperature until analysed.
The effect of three independent variables on the response was studied using a three-level, three-factor factorial Box-Behnken design (BBD) of Response Surface Methodology (RSM) (Ferreira, Duarte, Ribeiro, Queiroz, & Domingues, 2009). The three independent variable sets were feed moisture (%, X1), extrusion temperature (°C, X2), screw speed (rpm, X3), and each variable was set at the three levels. The range and levels of the variables investigated are given in Table 1. A total number of 17 experiments were designed (Table 2). Each experiment was performed in triplicate and the soluble dietary fibre content of soybean residue (%) was taken as the response, Y. The design matrix with 17 experimental runs in two blocks with five replicates of the midpoint is shown in Table 2. Regression analysis was performed for the experiment data and fitted to the empirical second order polynomial model, as shown in the following equation:
Y ¼ b0 þ
3 3 2 X 3 X X X bi X i þ bii X 2i þ bij X i X j i¼1
i¼1
ð1Þ
i¼1 j¼iþ1
2.3. Analytical methods 2.3.1. General methods Total nitrogen content was determined by the Kjeldahl method. A conversion factor of 6.25 was used to calculate protein on the basis of nitrogen. Oil was extracted for 24 h with diethyl ether in a Soxhlet system. Ash was determined by incineration in a furnace at 550 °C and weighed. In all cases the AOAC (2005) methods were followed.
where Y is the response variable, b0 bi bii and bij are the regression coefficients of variables for constant, linear, quadratic, and interaction regression terms, respectively; Xi and Xj are the coded values of the independent variables. The fitted polynomial equation is expressed as surface and contour plots in order to visualise the relationship between the response and experimental levels of each factor and to deduce the optimum conditions (Triveni, Shamala, & Rastogi, 2001). 2.5. Statistical analysis
2.3.2. Determination of dietary fibre content The contents of TDF, SDF and IDF in unextruded and extruded soybean residue were determined according to the AOAC 991.43 enzymatic–gravimetric method (AOAC, 2005). In brief, dried power samples were first gelatinized with heat stable a-amylase (95 °C, 35 min). After gelatinization, the samples were digested with protease and amyloglucosidase to remove protein and starch in the samples. Subsequently, IDF was filtered and washed with 60 °C distilled water. The filtrate and washed water were combined and added with four volumes of 95% ethanol to precipitate the SDF. The residues were weighed after drying at 105 °C in a hot air oven. TDF was calculated as the sum of IDF and SDF. 2.3.3. Water retention capacity (WRC) Fifteen millilitres of distilled water was added to 250 mg of sample in a 15 mL centrifuge tube. The sample was stirred and left at room temperature for 1 h. After centrifugation at 3000g for 20 min, the supernatant was discarded, the residue was weighed and WRC was calculated as g water per g of dry sample (Robertson et al., 2000). 2.3.4. Oil retention capacity (ORC) The same protocol as above was followed, but using commercial virgin olive instead of water. ORC was expressed as g olive oil retained per g of dry sample (Robertson et al., 2000). 2.3.5. Swelling capacity (SC) The sample (250 mg) was weighed in a 10 mL measuring cylinder and 5 mL distilled water, containing 0.02% sodium azide added. Then, it was stirred gently to eliminate trapped air bubbles and left on a level surface at room temperature overnight to allow sample to settle. Finally, the volume (mL) occupied by the sample was measured and SC was expressed as mL per g of dry sample (Robertson et al., 2000).
All experiments were carried out in triplicates. Analysis of variance of the results was performed using the Design-Expert 7.1 software (Statease Inc., Minneapolis, USA). The significances of all terms in the polynomial were judged statistically by computing the F-value at a probability (p) of 0.01 and 0.05. All calculations and graphics were performed using the Origin7.0 software. Table 1 The range of independent variables and their corresponding levels. Independent variables
Symbol
Feed moisture (%) Extrusion temperature (°C) Screw speed (rpm)
Coded factor level
Coded
1
0
1
X1 X2 X3
25 90 160
30 110 180
35 130 200
Table 2 Design and results of experiment. Run
Feed moisture X1
Extrusion temperature X2
Screw speed X3
The content of SDF (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
1 1 0 0 0 0 0 1 0 0 0 1 1 1 1 1 0
0 1 0 1 0 0 0 0 1 1 1 1 0 1 1 0 0
1 0 0 1 0 0 0 1 1 1 1 0 1 0 0 1 0
11.13 10.98 12.56 11.46 12.38 12.43 12.55 10.59 11.15 10.55 9.25 9.58 11.59 10.68 11.73 10.81 12.68
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889
Temperature is one of the factors affecting extrusion experiment effectiveness. According to the previous studies, the effect of extrusion temperature at 70, 90, 110, 130, and 150 °C was studied when the other extrusion conditions were set as follows: screw speed 180 rpm, feed moisture 30% (Fig. 1A). The content of SDF increased with an increase in the extrusion temperature and reached the maximum at 110 °C. However, when the extrusion temperature continued to increase, the content of SDF was rapidly decreased. This may be explained which the accelerated depolymerization of polysaccharides’ glucosidic bonds induced by increased temperature. So it resulted in an improvement on the solubility of the dietary fibre (Li, Long, Peng, Ming, & Zhao, 2012). But a higher extrusion temperature (P110 °C) may be cause material burnt and agglomerates in the barrel, puffing uneven and reduce the content of SDF, the twin-screw extruder was even bunged. Therefore, 90, 110, and 130 °C were chosen for the coded extrusion temperature variable levels at 1, 0, and +1, respectively. The influence of different screw speed on the content of SDF was investigated at 140, 160, 180, 200, and 220 rpm when the other extrusion conditions were set as follows: extrusion temperature 90 °C, feed moisture 30%. As shown in Fig. 1B, the content of SDF significantly increased from 8.99% to 10.88% with the screw speed increasing from 140 to 180 rpm. The maximum content (10.88%) of SDF was observed when the screw speed was 180 rpm. Beyond that screw speed range, the contents of SDF changed very little. The possible reason for this result may be that the higher the screw speed, the higher pressure in machine barrel, and so higher the pressure between material and machine barrel, material and screw, material and material, what indicates the SDF level rises in extruded products is under this condition, the large the large molecules are cracked easily, which amplifies the degree of decomposition of fibre material molecules, thus transform into smaller moleculars that contains many water-solubility parts. While the screw speed is overhigh, the material cannot hold long in machine barrel, which is not good for the rising of SDF content (Larrea, Chang, & Martinez Bustos, 2005). Therefore, 160, 180, and 200 rpm were selected as the three variable levels for the screw speed. Feed moisture also presents a positive effect on the content of SDF. It has been reported that the adequate feed moisture conduce to transport of the materials in the extruder (Valentina, Paul, Andrew, & Senol, 2009). The effect of different feed moisture on the content of SDF was examined at 20%, 25%, 30%, 35%, and 40% when the other extrusion conditions were set as follows: extrusion temperature 90 °C, screw speed 180 rpm (Fig. 1C). It showed that the content of SDF increased as the feed moisture ascended from 20% to 30%, the maximum content of SDF (10.88%) was observed when the feed moisture was 30%, after this point, the content of SDF started to decrease with the increasing of the feed moisture. Feed moisture can play an important role in affecting the pressure in cavity and shearing force. The low moisture have a advantage to enlarge pressure in machine barrel, frictional force and shearing force, therefore in favour of promoting SDF, but overlow will cause clogs machinery, which is useless to industrial production. Therefore, the three design levels selected for the feed moisture variable were 25%, 30%, and 35%, respectively.
A
13
12
Content of SDF (%)
3.1. Determining levels for independent variables
raw material (Liu, Miao, Wen, & Sun, 2009). Table 2 presents the value of responses (content of SDF) at different experimental combination for coded variables. By applying multiple regression
11
10
9
8 60
B
3.2.1. Statistical analysis and the model fitting RSM optimization is more advantageous than the traditional single parameter optimization in that it saves time, space and
100
120
140
160
12
11
10
9
8 120
140
160
180
200
220
240
Screw speed (rpm)
C
12
11
10
9
8
7 15
3.2. Response surface optimization of extrusion conditions
80
Extrusion temperature ( )
Content of SDF (%)
3. Results and discussion
Content of SDF (%)
886
20
25
30
35
40
45
Feed moisture (%) Fig. 1. Effects of twin-screw extrusion on the content of SDF. The three univariate tests were extrusion temperature (A), screw speed (B), feed moisture (C). The values represent the mean of triplicate experiments and the error bars represent standard deviation.
887
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Table 3 Analysis of variance (ANOVA) for the experimental results. Source
Sum of squares
Model X1 X2 X3 X1X2 X1X3 X2X3 X12 X22 X32 Residual Lack of fit Pure error Cor Total R2 Adj R2 C.V.%
16.58 1.26 3.46 0.66 0.03 0.01 0.25 1.92 5.12 2.80 0.22 0.16 0.06 16.80 0.9872 0.9707 1.55
Estimated coefficients 0.40 0.66 0.29 0.088 0.06 0.25 0.68 1.10 0.81
analysis on the experimental data, the response variable and the test variables are related by the following second-order polynomial equation:
Y ¼ 12:52 þ 0:40X 1 þ 0:66X 2 þ 0:29X 3 0:088X 1 X 2 þ 0:060X 2 X 3 0:25X 1 X 3 0:68X 21 1:10X 22 0:81X 23
ð2Þ
The results of analysis of variance for the BBD are shown in Table 3. The coefficient of determination (R2) of the model was 0.9872, which indicated that only 1.28% of the total variation was not explained by the model. The value of the adjusted determination coefficient (Adj R2 = 0.9707) also confirmed that the model was highly significant. The coefficient of variation (C.V.) of less than 5% indicated that the BBD designed model was reproducible (Mason, Gunst, & Hess, 1989; Wanasundara & Shahidi, 1996). In addition, Table 3 also shows the regression coefficients of the intercept, linear, and interaction terms of the model and the significance of each coefficient was determined using P-value. The Pvalue was used as a tool to check the significance of each coefficient, and the smaller the P-value was, the more significant the corresponding coefficient was (Guo, Zou, & Sun, 2010). According to Table 3, it was evident that the linear coefficients (X1, X2, X3), quadratic term coefficients (X12, X22, X32), and cross product coefficients (X2X3) were significant, with very small P-value (P < 0.05). The other term coefficients were not significant (P > 0.05). 3.2.2. Optimization of extrusion conditions The three-dimensional surface plots were obtained according to Eq. (2) that it can be used to determine optimal levels of the variables, and the results of content of SDF affected by extrusion temperature, screw speed, and feed moisture are presented in Fig. 2. Fig. 2A shows the content of SDF affected by different feed moisture and extrusion temperature, when the screw speed was fixed at 0 level. It can be seen that the content of SDF increased with extrusion temperature and feed moisture increasing, and the maximum content of SDF can be obtained when extrusion temperature and feed moisture were 114.57 °C and 31.37%, respectively. Fig. 2B shows the effect of the feed moisture and screw speed on the content of SDF at a fixed extrusion temperature of 110 °C. The content of SDF increased with the increasing of screw speed, and reached the peak value rapidly at screw speed 182.95 rpm, then followed by a decline with the further increase of screw speed. The interaction between the extrusion temperature and screw speed is shown in Fig. 2C at a fixed feed moisture of 30%. The extrusion temperature and screw speed used both had a positive impact on the content of SDF. The content of SDF increased with the increasing of
df
Mean square
F Value
Prob >F
9 1 1 1 1 1 1 1 1 1 7 3 4 16
1.84 1.26 3.46 0.66 0.03 0.01 0.25 1.92 5.12 2.80 0.03 0.05 0.02
59.93 40.85 112.48 21.32 1.00 0.47 7.97 62.39 166.46 90.96
<0.0001 0.0004 <0.0001 0.0024 0.3515 0.5158 0.0257 <0.0001 <0.0001 <0.0001
3.81
0.1145
screw speed, and reached the peak value rapidly at screw speed 182.95 rpm, then dropped from 182.95 to 200 rpm. According to the regression coefficients significance of the quadratic polynomial model, the optimal extrusion conditions were obtained by using response surface methodology as follows: extrusion temperature, 114.57 °C; feed moisture, 31.37%; and screw speed 182.95 rpm. 3.2.3. Verification of predictive model In order to facilitate the actual production, the modified optimal conditions were set as follows: extrusion temperature, 115 °C; feed moisture, 31%; and screw speed 180 rpm. Under these conditions, the rechecking experiment was performed to ensure the predicted result was not biased toward the practical value. A mean value of 12.65 ± 0.07 (n = 3) was obtained from real experiments, while the predicted value was 12.68%, demonstrated the validity of the RSM model and the model was adequate for the extrusion process, since there was no significant (p > 0.05) differences between them. 3.3. Composition of unextruded and extruded soybean residue The proximate composition of soybean residue is shown in Table 4. The contents of protein, fat, ash, and total dietary fibre in soybean residue changed very little when it was extruded. While the content of SDF increased from 2.05% to 12.65%, the IDF content decreased from 60.82% to 50.39%. Moreover, the amount of SDF increased was basically equal to the amount of IDF decreased which indicated that the increase in SDF was mainly from the degradation of IDF. These results were in accordance with MateosAparicio’s study (Mateos-Aparicio et al., 2010). 3.4. Effect of extrusion on physicochemical properties of dietary fibre in soybean residue The effect of extrusion on physicochemical properties of dietary fibre in soybean residue are as follows. The results indicated that the WRC (10.51 g/g), ORC (97.08 g/g) and SC (6.13 mL/g) of dietary fibre from extruded soybean residue were significantly higher than the WRC (7.99 g/g), ORC (77.42 g/g) and SC (5.79 mL/g) of dietary fibre from unextruded soybean residue. The possible reason for this result may be that heating might modify the structural characteristics of the fibre, hence facilitating its water and oil uptake (Figuerola, Hurtado, Estevez, Chiffelle, & Asenjo, 2005), while the higher swelling capacity shown in SDF from extruded soybean residue could be explained by its higher molecular weight and SDF content (Zhang et al., 2011). The extrusion process improved the
888
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Table 4 Components of soybean residue.* Soybean residue Protein Fat Ash SDF IDF DF
a
20.18 ± 0.16 7.35 ± 0.22a 3.48 ± 0.13a 2.05 ± 0.17a 60.82 ± 0.26a 63.03 ± 0.39a
Extruded soybean residue 19.92 ± 0.23a 7.33 ± 0.38a 3.53 ± 0.24a 12.65 ± 0.04b 50.39 ± 0.13b 63.09 ± 0.16a
For each row, values followed by the different letters indicate significant differences (P < 0.05). * The extrudation parameters are 115 °C, 180 rpm and 31% of moisture. Values are expressed as mean ± standard deviation (n = 3).
4. Conclusion In the present paper, the content of SDF (12.65%) prepared from extruded soybean residue was significantly higher than the content of SDF (2.05%) prepared from soybean residue. It indicated that the twin-screw extrusion technology can significantly improve the content of SDF in soybean residue. At the same time, the extrusion efficiency of this process was higher than the single-screw extruder, because of the screw speed was increased, so it reduced the extrusion time greatly; in addition, the extrusion temperature of 110 °C was lower than the single-srew extruder, which was required lower energy and it was also benefited to industrialise.
Acknowledgements The authors gratefully acknowledge the financial support provided by Natural Science Foundation of Heilongjiang Province, China (No. ZD200902). The authors especially appreciate for valuable and critical comments by the editors and reviewers, which greatly improve the quality of the manuscript.
References
Fig. 2. Response surface plots showing the effects of the variables on the content of SDF. The three independent variables set were extrusion temperature (A), screw speed (B), feed moisture (C).
physicochemical properties of dietary fibre from soybean residue and functional characteristics were enhanced obviously. It was in accordance with the earlier reported values (Zhang et al., 2011).
AACC Report. (2000). The definition of dietary fibre. Cereal Foods World, 46, 112–129. AOAC. (2005). Official Methods of Analysis of the AOAC International. Gaithersburg, MD: Association of Official Analytical Chemists. Esposito, Fabrizio, Arlotti, Guido, Bonifati, Angela Maria, Napolitano, Aurora, Vitate, Davide, & Fogliano, Vincenzo (2005). Antioxidant activity and dietary fibre in durum wheat bran by-products. Food Research International, 38, 1167–1173. Faraj, A., Vasanthan, T., & Hoover, R. (2004). The effect of extrusion cooking on resistant starch formation in waxy and regular barley flours. Food Research International, 37, 517–525. Farouk, A., Pudil, F., Janda, V., & Pokoeny, J. (2000). Effect of amino acids on the composition and properties of extruded mixtures of wheat flour and glucose. Nahrung, 44, 188–192. Ferreira, S., Duarte, A. P., Ribeiro, M. H. L., Queiroz, J. A., & Domingues, F. C. (2009). Response surface optimization of enzymatic hydrolysis of Cistus iadanifer and Cytisus striatus for bioethanol production. New Biotechnology, 45, 260–261. Figuerola, F., Hurtado, M. L., Estevez, A. M., Chiffelle, I., & Asenjo, F. (2005). Fibre concentrates from apple pomace and citrus peel as potential fibre sources for food enrichment. Food Chemistry, 91, 395–401. Guo, X., Zou, X., & Sun, M. (2010). Optimization of extraction process by response surface methodology and preliminary characterization of polysaccharides from Phellinus igniarius. Carbohydrate Polymers, 80, 344–349. Kim, J. H., Tanhehco, E. j., & Ng, P. K. W. (2006). Effect of extrusion conditions on resistant starch formation from pastry wheat flour. Food Chemistry, 99, 718–723. Larrea, M. A., Chang, Y. K., & Martinez Bustos, F. (2005). Effect of some operational extrusion parameters on the constituents of orange pulp. Food Chemistry, 89, 301–308. Li, Huiqin, Long, Daoqi, Peng, Jianlin, Ming, Jian, & Zhao, Guohua (2012). Anovel insitu enhanced blasting extrusion technique – Extrudate analysis and optimization of processing conditions with okara. Innovative Food Science and Emerging Technologies, 60, 211–219. Liu, J. C., Miao, S., Wen, X. C., & Sun, Y. X. (2009). Optimization of polysaccharides (ABP) extraction from the fruiting bodies of Agaricus blazei Murill using response surface methodology (RSM). Carbohydrate Polymers, 78, 704–709.
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Lou, H. W., & Chi, Y. J. (2009). Optimization of technology for preparing soluble dietary fiber from extruded soybean residue. Transactions of the CSAE, 25, 285–289. Mason, R. L., Gunst, R. F., & Hess, J. L. (1989). Statistical design and analysis of experiments: With applications to engineering and science. Wiley series in probability and mathematical statistics. New York: John Wiley and sons. Mateos-Aparicio, P., Mateos-Peinado, C., & Ruperez, P. (2010). High hydrostatic pressure improves the functionality of dietary fiber in okara by-product from soybean. Innovative Food Science and Emerging Technologies, 11, 445–450. Robertson, James A., de Monredon, Francois D., Dysseler, Patrick, Guillon, Fabienne, Amado, Renato, & Thibault, Jean-Francols (2000). Hydration properties of dietary fiber and resistant starch: A European collaborative study. LWT – Food Science and Technology, 33, 72–79. Triveni, R., Shamala, T. R., & Rastogi, N. K. (2001). Optimised production and utilisation of expolysaccharide from Agrobacterium radiobacter. Process Biochemistry, 36(8), 787–795.
889
Valentina, S., Paul, A., Andrew, P., & Senol, l. (2009). The effect of extrusion cooking using different water feed rates on the quality of ready-to-eat snacks made from food by-products. Food Chemistry, 114, 226–232. Valentina, S., Paul, A., Andrew, P., & Senol, l. (2010). The advantage of using extrusion processing for increasing dietary fibre level in gluten-free products. Food Chemistry, 121, 156–164. Vasanthan, Thava, Gaosong, Jiang, Yeung, Judy, & Li, Jihong (2002). Dietary fiber profile of barely flour as affected by extrusion cooking. Food Chemistry, 77, 35–40. Wanasundara, P. K. J. P. D., & Shahidi, F. (1996). Optimization of hexamtaphosphateassisted extraction of flaxseed proteins using response surface methodology. Journal of Food Science, 61, 604–607. Zhang, M., Bai, X., & Zhang, Z. (2011). Extrusion process improves the functionality of soluble dietary fiber in oat bran. Journal of Cereal Science, 54, 98–103.
Contents lists available at SciVerse ScienceDirect
Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Effects of twin-screw extrusion on soluble dietary fibre and physicochemical properties of soybean residue Yan Jing, Yu-Jie Chi ⇑ Department of Food Science, Northeast Agricultural University, Harbin 150030, China Education Ministry’s and Provincial Key Laboratory of Soybean Biology, Harbin 150030, China
a r t i c l e
i n f o
Article history: Received 4 August 2012 Received in revised form 29 November 2012 Accepted 2 December 2012 Available online 8 December 2012 Keywords: Soybean residue Twin-screw extrusion Soluble dietary fibre Physicochemical properties
a b s t r a c t Extrusion cooking technology was applied for soluble dietary fibre extraction from soybean residue. Response surface methodology (RSM) was used to optimise the effects of extrusion parameters, namely extrusion temperature (90–130 °C), feed moisture (25–35%) and screw speed (160–200 rpm) on the content of soluble dietary fibre. According to the regression coefficients significance of the quadratic polynomial model, the optimum extrusion parameters were as follows: extrusion temperature, 115 °C; feed moisture, 31%; and screw speed, 180 rpm. Under these conditions, the soluble dietary fibre content of soybean residue could reach to 12.65% which increased 10.60% compared with the unextruded soybean residue. In addition, the dietary fibre in extrude soybean residue had higher water retention capacity, oil retention capacity and swelling capacity than those of dietary fibre in unextruded soybean residue. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The definition of dietary fibre (DF) proposed by the American Association of Cereal Chemists (AACC) defines DF as being made up of edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine (AACC Report, 2000). According to the solubility in water, total dietary fibre (TDF) can be categorised into two groups, namely soluble dietary fibre (SDF) and insoluble dietary fibre (IDF) (Vasanthan, Gaosong, Yeung, & Li, 2002). Many studies have shown that DF plays different physiological roles in human health and the SDF appears to be more effective than IDF in many healthy aspects (Esposito et al., 2005; Lou & Chi, 2009). But the most of crude dietary fibre are IDF, while the content of SDF are very low. Therefore, it has special significance to improve the SDF content of crude dietary fibre. Soybean residue is the main by-product from soymilk and tofu preparation, which is a good dietary fibre resource (Mateos-Aparicio, Mateos-Peinado, & Ruperez, 2010). The content of TDF in soybean residue is about 60%, while the SDF content is only approximate 2–3%. Extrusion cooking is a thermal processing that involves the application of high heat, high pressure, and shear forces to an uncooked mass, such as cereal foods (Kim, Tanhehco, & Ng, 2006). Extrusion technology is a new economical processing ⇑ Corresponding author at: Department of Food Science, Northeast Agricultural University, Harbin 150030, China. Tel./fax: +86 451 55191793. E-mail address: [email protected] (Y.-J. Chi). 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.12.003
methods, it can achieve protein, starch and cellulose polymer transformation directly or indirectly in a short time (Valentina, Paul, Andrew, & Senol, 2010). Extrusion of cereal-based products has advantages over other usual processing methods because of low cost, short time, high productivity, versatility, unique product shapes, and energy savings (Faraj, Vasanthan, & Hoover, 2004; Farouk, Pudil, Janda, & Pokoeny, 2000). In recent years, a number of researchers use barley flour and oat bran to prepare SDF (Vasanthan et al., 2002; Zhang, Bai, & Zhang, 2011). But there has no been relative reports about that using twin-screw extruder to prepare SDF from soybean residue. The results of our previous study (extrusion parameter: extrusion temperature, 160 °C; feed moisture, 20%; and screw speed, 175 rpm) also showed that the extrusion temperature of single screw extruder was too high, which consumed more energy and it is not benefit for industrial production. Therefore, the purpose of the present study was to employ response surface methodology to optimise the effect of different extrusion conditions on the content of SDF in soybean residue, thereby providing a reference for the preparation of high yield of soluble dietary fibre and its industrial production. 2. Materials and methods 2.1. Materials Soybean residue was supplied by bean products factory of Northeast Agricultural University (Harbin, China). Heat stable a-amylase, Protease and Amyloglucosidase were obtained from Sigma Chemical Company. All the other reagents were of analytical grade.
885
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889
2.2. Extrusion experiments
2.4. Experimental design
Soybean residue sample (1.5 kg) was extruded with a DS56-III twin-screw co-rotating, self-wiping extruder (Jinan Saixin Machinery Co., Jinan, China). The barrel diameter and length were 65 and 1008 mm, respectively, the screw speed up to 250 rpm. A screw configuration that was a standard design for processing cereals and flour-based products was used. This screw profile was made up of conveying self- wiping elements and the center distance of two screw was 56 mm. The feed moisture of 20%, 25%, 30%, 35% and 40% were selected according to the results of pre-experiments and references. The extrusion temperature was adjusted to 70, 90, 110, 130 and 150 °C, while screw speed of 140, 160, 180, 200 and 220 rpm were employed. The extruded soybean residue was dried in an oven at temperature of 60 °C, ground in a high speed disintegrator (Dade pharmaceuticals company, Wenzhou, China) to obtain a fine power (Particle size: 0.425 mm), then stored at room temperature until analysed.
The effect of three independent variables on the response was studied using a three-level, three-factor factorial Box-Behnken design (BBD) of Response Surface Methodology (RSM) (Ferreira, Duarte, Ribeiro, Queiroz, & Domingues, 2009). The three independent variable sets were feed moisture (%, X1), extrusion temperature (°C, X2), screw speed (rpm, X3), and each variable was set at the three levels. The range and levels of the variables investigated are given in Table 1. A total number of 17 experiments were designed (Table 2). Each experiment was performed in triplicate and the soluble dietary fibre content of soybean residue (%) was taken as the response, Y. The design matrix with 17 experimental runs in two blocks with five replicates of the midpoint is shown in Table 2. Regression analysis was performed for the experiment data and fitted to the empirical second order polynomial model, as shown in the following equation:
Y ¼ b0 þ
3 3 2 X 3 X X X bi X i þ bii X 2i þ bij X i X j i¼1
i¼1
ð1Þ
i¼1 j¼iþ1
2.3. Analytical methods 2.3.1. General methods Total nitrogen content was determined by the Kjeldahl method. A conversion factor of 6.25 was used to calculate protein on the basis of nitrogen. Oil was extracted for 24 h with diethyl ether in a Soxhlet system. Ash was determined by incineration in a furnace at 550 °C and weighed. In all cases the AOAC (2005) methods were followed.
where Y is the response variable, b0 bi bii and bij are the regression coefficients of variables for constant, linear, quadratic, and interaction regression terms, respectively; Xi and Xj are the coded values of the independent variables. The fitted polynomial equation is expressed as surface and contour plots in order to visualise the relationship between the response and experimental levels of each factor and to deduce the optimum conditions (Triveni, Shamala, & Rastogi, 2001). 2.5. Statistical analysis
2.3.2. Determination of dietary fibre content The contents of TDF, SDF and IDF in unextruded and extruded soybean residue were determined according to the AOAC 991.43 enzymatic–gravimetric method (AOAC, 2005). In brief, dried power samples were first gelatinized with heat stable a-amylase (95 °C, 35 min). After gelatinization, the samples were digested with protease and amyloglucosidase to remove protein and starch in the samples. Subsequently, IDF was filtered and washed with 60 °C distilled water. The filtrate and washed water were combined and added with four volumes of 95% ethanol to precipitate the SDF. The residues were weighed after drying at 105 °C in a hot air oven. TDF was calculated as the sum of IDF and SDF. 2.3.3. Water retention capacity (WRC) Fifteen millilitres of distilled water was added to 250 mg of sample in a 15 mL centrifuge tube. The sample was stirred and left at room temperature for 1 h. After centrifugation at 3000g for 20 min, the supernatant was discarded, the residue was weighed and WRC was calculated as g water per g of dry sample (Robertson et al., 2000). 2.3.4. Oil retention capacity (ORC) The same protocol as above was followed, but using commercial virgin olive instead of water. ORC was expressed as g olive oil retained per g of dry sample (Robertson et al., 2000). 2.3.5. Swelling capacity (SC) The sample (250 mg) was weighed in a 10 mL measuring cylinder and 5 mL distilled water, containing 0.02% sodium azide added. Then, it was stirred gently to eliminate trapped air bubbles and left on a level surface at room temperature overnight to allow sample to settle. Finally, the volume (mL) occupied by the sample was measured and SC was expressed as mL per g of dry sample (Robertson et al., 2000).
All experiments were carried out in triplicates. Analysis of variance of the results was performed using the Design-Expert 7.1 software (Statease Inc., Minneapolis, USA). The significances of all terms in the polynomial were judged statistically by computing the F-value at a probability (p) of 0.01 and 0.05. All calculations and graphics were performed using the Origin7.0 software. Table 1 The range of independent variables and their corresponding levels. Independent variables
Symbol
Feed moisture (%) Extrusion temperature (°C) Screw speed (rpm)
Coded factor level
Coded
1
0
1
X1 X2 X3
25 90 160
30 110 180
35 130 200
Table 2 Design and results of experiment. Run
Feed moisture X1
Extrusion temperature X2
Screw speed X3
The content of SDF (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
1 1 0 0 0 0 0 1 0 0 0 1 1 1 1 1 0
0 1 0 1 0 0 0 0 1 1 1 1 0 1 1 0 0
1 0 0 1 0 0 0 1 1 1 1 0 1 0 0 1 0
11.13 10.98 12.56 11.46 12.38 12.43 12.55 10.59 11.15 10.55 9.25 9.58 11.59 10.68 11.73 10.81 12.68
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889
Temperature is one of the factors affecting extrusion experiment effectiveness. According to the previous studies, the effect of extrusion temperature at 70, 90, 110, 130, and 150 °C was studied when the other extrusion conditions were set as follows: screw speed 180 rpm, feed moisture 30% (Fig. 1A). The content of SDF increased with an increase in the extrusion temperature and reached the maximum at 110 °C. However, when the extrusion temperature continued to increase, the content of SDF was rapidly decreased. This may be explained which the accelerated depolymerization of polysaccharides’ glucosidic bonds induced by increased temperature. So it resulted in an improvement on the solubility of the dietary fibre (Li, Long, Peng, Ming, & Zhao, 2012). But a higher extrusion temperature (P110 °C) may be cause material burnt and agglomerates in the barrel, puffing uneven and reduce the content of SDF, the twin-screw extruder was even bunged. Therefore, 90, 110, and 130 °C were chosen for the coded extrusion temperature variable levels at 1, 0, and +1, respectively. The influence of different screw speed on the content of SDF was investigated at 140, 160, 180, 200, and 220 rpm when the other extrusion conditions were set as follows: extrusion temperature 90 °C, feed moisture 30%. As shown in Fig. 1B, the content of SDF significantly increased from 8.99% to 10.88% with the screw speed increasing from 140 to 180 rpm. The maximum content (10.88%) of SDF was observed when the screw speed was 180 rpm. Beyond that screw speed range, the contents of SDF changed very little. The possible reason for this result may be that the higher the screw speed, the higher pressure in machine barrel, and so higher the pressure between material and machine barrel, material and screw, material and material, what indicates the SDF level rises in extruded products is under this condition, the large the large molecules are cracked easily, which amplifies the degree of decomposition of fibre material molecules, thus transform into smaller moleculars that contains many water-solubility parts. While the screw speed is overhigh, the material cannot hold long in machine barrel, which is not good for the rising of SDF content (Larrea, Chang, & Martinez Bustos, 2005). Therefore, 160, 180, and 200 rpm were selected as the three variable levels for the screw speed. Feed moisture also presents a positive effect on the content of SDF. It has been reported that the adequate feed moisture conduce to transport of the materials in the extruder (Valentina, Paul, Andrew, & Senol, 2009). The effect of different feed moisture on the content of SDF was examined at 20%, 25%, 30%, 35%, and 40% when the other extrusion conditions were set as follows: extrusion temperature 90 °C, screw speed 180 rpm (Fig. 1C). It showed that the content of SDF increased as the feed moisture ascended from 20% to 30%, the maximum content of SDF (10.88%) was observed when the feed moisture was 30%, after this point, the content of SDF started to decrease with the increasing of the feed moisture. Feed moisture can play an important role in affecting the pressure in cavity and shearing force. The low moisture have a advantage to enlarge pressure in machine barrel, frictional force and shearing force, therefore in favour of promoting SDF, but overlow will cause clogs machinery, which is useless to industrial production. Therefore, the three design levels selected for the feed moisture variable were 25%, 30%, and 35%, respectively.
A
13
12
Content of SDF (%)
3.1. Determining levels for independent variables
raw material (Liu, Miao, Wen, & Sun, 2009). Table 2 presents the value of responses (content of SDF) at different experimental combination for coded variables. By applying multiple regression
11
10
9
8 60
B
3.2.1. Statistical analysis and the model fitting RSM optimization is more advantageous than the traditional single parameter optimization in that it saves time, space and
100
120
140
160
12
11
10
9
8 120
140
160
180
200
220
240
Screw speed (rpm)
C
12
11
10
9
8
7 15
3.2. Response surface optimization of extrusion conditions
80
Extrusion temperature ( )
Content of SDF (%)
3. Results and discussion
Content of SDF (%)
886
20
25
30
35
40
45
Feed moisture (%) Fig. 1. Effects of twin-screw extrusion on the content of SDF. The three univariate tests were extrusion temperature (A), screw speed (B), feed moisture (C). The values represent the mean of triplicate experiments and the error bars represent standard deviation.
887
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Table 3 Analysis of variance (ANOVA) for the experimental results. Source
Sum of squares
Model X1 X2 X3 X1X2 X1X3 X2X3 X12 X22 X32 Residual Lack of fit Pure error Cor Total R2 Adj R2 C.V.%
16.58 1.26 3.46 0.66 0.03 0.01 0.25 1.92 5.12 2.80 0.22 0.16 0.06 16.80 0.9872 0.9707 1.55
Estimated coefficients 0.40 0.66 0.29 0.088 0.06 0.25 0.68 1.10 0.81
analysis on the experimental data, the response variable and the test variables are related by the following second-order polynomial equation:
Y ¼ 12:52 þ 0:40X 1 þ 0:66X 2 þ 0:29X 3 0:088X 1 X 2 þ 0:060X 2 X 3 0:25X 1 X 3 0:68X 21 1:10X 22 0:81X 23
ð2Þ
The results of analysis of variance for the BBD are shown in Table 3. The coefficient of determination (R2) of the model was 0.9872, which indicated that only 1.28% of the total variation was not explained by the model. The value of the adjusted determination coefficient (Adj R2 = 0.9707) also confirmed that the model was highly significant. The coefficient of variation (C.V.) of less than 5% indicated that the BBD designed model was reproducible (Mason, Gunst, & Hess, 1989; Wanasundara & Shahidi, 1996). In addition, Table 3 also shows the regression coefficients of the intercept, linear, and interaction terms of the model and the significance of each coefficient was determined using P-value. The Pvalue was used as a tool to check the significance of each coefficient, and the smaller the P-value was, the more significant the corresponding coefficient was (Guo, Zou, & Sun, 2010). According to Table 3, it was evident that the linear coefficients (X1, X2, X3), quadratic term coefficients (X12, X22, X32), and cross product coefficients (X2X3) were significant, with very small P-value (P < 0.05). The other term coefficients were not significant (P > 0.05). 3.2.2. Optimization of extrusion conditions The three-dimensional surface plots were obtained according to Eq. (2) that it can be used to determine optimal levels of the variables, and the results of content of SDF affected by extrusion temperature, screw speed, and feed moisture are presented in Fig. 2. Fig. 2A shows the content of SDF affected by different feed moisture and extrusion temperature, when the screw speed was fixed at 0 level. It can be seen that the content of SDF increased with extrusion temperature and feed moisture increasing, and the maximum content of SDF can be obtained when extrusion temperature and feed moisture were 114.57 °C and 31.37%, respectively. Fig. 2B shows the effect of the feed moisture and screw speed on the content of SDF at a fixed extrusion temperature of 110 °C. The content of SDF increased with the increasing of screw speed, and reached the peak value rapidly at screw speed 182.95 rpm, then followed by a decline with the further increase of screw speed. The interaction between the extrusion temperature and screw speed is shown in Fig. 2C at a fixed feed moisture of 30%. The extrusion temperature and screw speed used both had a positive impact on the content of SDF. The content of SDF increased with the increasing of
df
Mean square
F Value
Prob >F
9 1 1 1 1 1 1 1 1 1 7 3 4 16
1.84 1.26 3.46 0.66 0.03 0.01 0.25 1.92 5.12 2.80 0.03 0.05 0.02
59.93 40.85 112.48 21.32 1.00 0.47 7.97 62.39 166.46 90.96
<0.0001 0.0004 <0.0001 0.0024 0.3515 0.5158 0.0257 <0.0001 <0.0001 <0.0001
3.81
0.1145
screw speed, and reached the peak value rapidly at screw speed 182.95 rpm, then dropped from 182.95 to 200 rpm. According to the regression coefficients significance of the quadratic polynomial model, the optimal extrusion conditions were obtained by using response surface methodology as follows: extrusion temperature, 114.57 °C; feed moisture, 31.37%; and screw speed 182.95 rpm. 3.2.3. Verification of predictive model In order to facilitate the actual production, the modified optimal conditions were set as follows: extrusion temperature, 115 °C; feed moisture, 31%; and screw speed 180 rpm. Under these conditions, the rechecking experiment was performed to ensure the predicted result was not biased toward the practical value. A mean value of 12.65 ± 0.07 (n = 3) was obtained from real experiments, while the predicted value was 12.68%, demonstrated the validity of the RSM model and the model was adequate for the extrusion process, since there was no significant (p > 0.05) differences between them. 3.3. Composition of unextruded and extruded soybean residue The proximate composition of soybean residue is shown in Table 4. The contents of protein, fat, ash, and total dietary fibre in soybean residue changed very little when it was extruded. While the content of SDF increased from 2.05% to 12.65%, the IDF content decreased from 60.82% to 50.39%. Moreover, the amount of SDF increased was basically equal to the amount of IDF decreased which indicated that the increase in SDF was mainly from the degradation of IDF. These results were in accordance with MateosAparicio’s study (Mateos-Aparicio et al., 2010). 3.4. Effect of extrusion on physicochemical properties of dietary fibre in soybean residue The effect of extrusion on physicochemical properties of dietary fibre in soybean residue are as follows. The results indicated that the WRC (10.51 g/g), ORC (97.08 g/g) and SC (6.13 mL/g) of dietary fibre from extruded soybean residue were significantly higher than the WRC (7.99 g/g), ORC (77.42 g/g) and SC (5.79 mL/g) of dietary fibre from unextruded soybean residue. The possible reason for this result may be that heating might modify the structural characteristics of the fibre, hence facilitating its water and oil uptake (Figuerola, Hurtado, Estevez, Chiffelle, & Asenjo, 2005), while the higher swelling capacity shown in SDF from extruded soybean residue could be explained by its higher molecular weight and SDF content (Zhang et al., 2011). The extrusion process improved the
888
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Table 4 Components of soybean residue.* Soybean residue Protein Fat Ash SDF IDF DF
a
20.18 ± 0.16 7.35 ± 0.22a 3.48 ± 0.13a 2.05 ± 0.17a 60.82 ± 0.26a 63.03 ± 0.39a
Extruded soybean residue 19.92 ± 0.23a 7.33 ± 0.38a 3.53 ± 0.24a 12.65 ± 0.04b 50.39 ± 0.13b 63.09 ± 0.16a
For each row, values followed by the different letters indicate significant differences (P < 0.05). * The extrudation parameters are 115 °C, 180 rpm and 31% of moisture. Values are expressed as mean ± standard deviation (n = 3).
4. Conclusion In the present paper, the content of SDF (12.65%) prepared from extruded soybean residue was significantly higher than the content of SDF (2.05%) prepared from soybean residue. It indicated that the twin-screw extrusion technology can significantly improve the content of SDF in soybean residue. At the same time, the extrusion efficiency of this process was higher than the single-screw extruder, because of the screw speed was increased, so it reduced the extrusion time greatly; in addition, the extrusion temperature of 110 °C was lower than the single-srew extruder, which was required lower energy and it was also benefited to industrialise.
Acknowledgements The authors gratefully acknowledge the financial support provided by Natural Science Foundation of Heilongjiang Province, China (No. ZD200902). The authors especially appreciate for valuable and critical comments by the editors and reviewers, which greatly improve the quality of the manuscript.
References
Fig. 2. Response surface plots showing the effects of the variables on the content of SDF. The three independent variables set were extrusion temperature (A), screw speed (B), feed moisture (C).
physicochemical properties of dietary fibre from soybean residue and functional characteristics were enhanced obviously. It was in accordance with the earlier reported values (Zhang et al., 2011).
AACC Report. (2000). The definition of dietary fibre. Cereal Foods World, 46, 112–129. AOAC. (2005). Official Methods of Analysis of the AOAC International. Gaithersburg, MD: Association of Official Analytical Chemists. Esposito, Fabrizio, Arlotti, Guido, Bonifati, Angela Maria, Napolitano, Aurora, Vitate, Davide, & Fogliano, Vincenzo (2005). Antioxidant activity and dietary fibre in durum wheat bran by-products. Food Research International, 38, 1167–1173. Faraj, A., Vasanthan, T., & Hoover, R. (2004). The effect of extrusion cooking on resistant starch formation in waxy and regular barley flours. Food Research International, 37, 517–525. Farouk, A., Pudil, F., Janda, V., & Pokoeny, J. (2000). Effect of amino acids on the composition and properties of extruded mixtures of wheat flour and glucose. Nahrung, 44, 188–192. Ferreira, S., Duarte, A. P., Ribeiro, M. H. L., Queiroz, J. A., & Domingues, F. C. (2009). Response surface optimization of enzymatic hydrolysis of Cistus iadanifer and Cytisus striatus for bioethanol production. New Biotechnology, 45, 260–261. Figuerola, F., Hurtado, M. L., Estevez, A. M., Chiffelle, I., & Asenjo, F. (2005). Fibre concentrates from apple pomace and citrus peel as potential fibre sources for food enrichment. Food Chemistry, 91, 395–401. Guo, X., Zou, X., & Sun, M. (2010). Optimization of extraction process by response surface methodology and preliminary characterization of polysaccharides from Phellinus igniarius. Carbohydrate Polymers, 80, 344–349. Kim, J. H., Tanhehco, E. j., & Ng, P. K. W. (2006). Effect of extrusion conditions on resistant starch formation from pastry wheat flour. Food Chemistry, 99, 718–723. Larrea, M. A., Chang, Y. K., & Martinez Bustos, F. (2005). Effect of some operational extrusion parameters on the constituents of orange pulp. Food Chemistry, 89, 301–308. Li, Huiqin, Long, Daoqi, Peng, Jianlin, Ming, Jian, & Zhao, Guohua (2012). Anovel insitu enhanced blasting extrusion technique – Extrudate analysis and optimization of processing conditions with okara. Innovative Food Science and Emerging Technologies, 60, 211–219. Liu, J. C., Miao, S., Wen, X. C., & Sun, Y. X. (2009). Optimization of polysaccharides (ABP) extraction from the fruiting bodies of Agaricus blazei Murill using response surface methodology (RSM). Carbohydrate Polymers, 78, 704–709.
Y. Jing, Y.-J. Chi / Food Chemistry 138 (2013) 884–889 Lou, H. W., & Chi, Y. J. (2009). Optimization of technology for preparing soluble dietary fiber from extruded soybean residue. Transactions of the CSAE, 25, 285–289. Mason, R. L., Gunst, R. F., & Hess, J. L. (1989). Statistical design and analysis of experiments: With applications to engineering and science. Wiley series in probability and mathematical statistics. New York: John Wiley and sons. Mateos-Aparicio, P., Mateos-Peinado, C., & Ruperez, P. (2010). High hydrostatic pressure improves the functionality of dietary fiber in okara by-product from soybean. Innovative Food Science and Emerging Technologies, 11, 445–450. Robertson, James A., de Monredon, Francois D., Dysseler, Patrick, Guillon, Fabienne, Amado, Renato, & Thibault, Jean-Francols (2000). Hydration properties of dietary fiber and resistant starch: A European collaborative study. LWT – Food Science and Technology, 33, 72–79. Triveni, R., Shamala, T. R., & Rastogi, N. K. (2001). Optimised production and utilisation of expolysaccharide from Agrobacterium radiobacter. Process Biochemistry, 36(8), 787–795.
889
Valentina, S., Paul, A., Andrew, P., & Senol, l. (2009). The effect of extrusion cooking using different water feed rates on the quality of ready-to-eat snacks made from food by-products. Food Chemistry, 114, 226–232. Valentina, S., Paul, A., Andrew, P., & Senol, l. (2010). The advantage of using extrusion processing for increasing dietary fibre level in gluten-free products. Food Chemistry, 121, 156–164. Vasanthan, Thava, Gaosong, Jiang, Yeung, Judy, & Li, Jihong (2002). Dietary fiber profile of barely flour as affected by extrusion cooking. Food Chemistry, 77, 35–40. Wanasundara, P. K. J. P. D., & Shahidi, F. (1996). Optimization of hexamtaphosphateassisted extraction of flaxseed proteins using response surface methodology. Journal of Food Science, 61, 604–607. Zhang, M., Bai, X., & Zhang, Z. (2011). Extrusion process improves the functionality of soluble dietary fiber in oat bran. Journal of Cereal Science, 54, 98–103.